Not all land grants your ancestors may have been a part of date from the period that the United States owned the territory, and states such as Texas and Missouri, to name a couple, were owned by other countries who gave out land to settlers. I discovered this website when I was considering a Texas based research project. It is similar to the BLM Land Grant site , just specific to Texas.
Link: Texas Land Grant Search
Tomorrow, I plan on posting about England's Old Poor Law.